Mesoscale Discussion 278

Issued

Mar 27, 2021, 11:55 AM CDT (16:55 UTC)

Expired

Mar 27, 2021, 2:30 PM CDT

In force

3 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...tornado watch likely

Chance of a watch

80%

The Columbus AFB radar (KGWX), 139 km from the middle of the area, began a volume at 16:55 UTC, the scan nearest the moment this went out.

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• Tornado Watch 59Mar 27, 1:45 PM CDT

262 
ACUS11 KWNS 271655
SWOMCD
SPC MCD 271655 
TNZ000-GAZ000-ALZ000-MSZ000-ARZ000-271930-

Mesoscale Discussion 0278
NWS Storm Prediction Center Norman OK
1155 AM CDT Sat Mar 27 2021

Areas affected...Portions of eastern AR...much of TN...northern
MS/AL...and extreme northwestern GA

Concerning...Severe potential...Tornado Watch likely 

Valid 271655Z - 271930Z

Probability of Watch Issuance...80 percent

SUMMARY...The severe threat should gradually increase this afternoon
along and south of a front. A few tornadoes, large hail, and
damaging wind gusts all appear possible. Watch issuance is likely by
early afternoon.

DISCUSSION...16Z surface analysis shows a convectively reinforced
front draped generally west to east across southern TN. Scattered to
numerous showers and thunderstorms are ongoing mainly along/north of
this front owing to continued southwesterly low-level warm
advection. Low-level moisture is expected to increase further
through the early afternoon as surface dewpoints reach the mid/upper
60s across the warm sector. Modestly steepened mid-level lapse rates
should also overspread parts of eastern AR into western TN and
northern MN/AL. Continued modest diurnal heating combined with the
rich low-level moisture and steepening lapse rates aloft will likely
support the development of 1500-2500 J/kg of MLCAPE by peak
afternoon heating along/south of the front.

Large-scale forcing appears nebulous with an upper trough remaining
well to the west of this region. Still, the front may lift very
slowly northward across TN through the afternoon with persistent
25-35 kt of southwesterly low-level flow. A broad swath of 50-60 kt
of west-southwesterly winds at mid levels will foster around 40-50
kt of effective bulk shear. This will likely support supercell
structures and small bowing line segments with any storms that can
develop along/south of the warm front. Large hail will be a concern
with any discrete storms given the favorable environment, and some
isolated very large hail of 2+ inches in diameter appears possible
where the greatest instability can develop (likely eastern
AR/western TN/northern MS). At least isolated damaging wind gusts
may also occur if storms can congeal and move eastward along the
front while remaining surface based.

Although the low-level flow is not overly strong at the moment, it
should gradually strengthen later this afternoon. Regardless, around
150-200 m2/s2 of effective SRH will likely support updraft rotation,
and a few tornadoes may occur with any supercells that can form. The
tornado potential will likely be maximized along the warm front,
where surface winds should be backed to a more east-southeasterly
direction, enhancing low-level shear. A strong tornado or two also
appears possible, mainly later this afternoon/early evening as
low-level winds gradually strengthen. Current expectations are for
storms to gradually increase in coverage and intensity through the
early afternoon. Accordingly, a tornado watch will likely be needed
in the next couple of hours.

..Gleason/Thompson.. 03/27/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...MRX...FFC...OHX...HUN...MEG...

LAT...LON   34409041 34649092 35479090 35889028 36088795 35898647
            35808454 35568417 34928439 34638551 34388815 34348944
            34409041

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.